A wide bandgap semiconductor represented by GaN or SiC has excellent characteristics such as high-speed switching and low-on resistance, compared to a silicon semiconductor. On the other hand, an element using the wide bandgap semiconductor exhibits a normally-on characteristic in which a drain current flows even if a gate voltage is 0 V, or a normally-off characteristic in which a threshold voltage is low such as about 2 V. In order to surely turn off the element, it is necessary that the gate voltage is driven to a negative voltage, whereby a driver circuit that feeds the negative gate voltage is needed.
Non-Patent Document 1 describes a buffer circuit that is driven by negative gate/bias voltage.
Patent Document 1 describes a semiconductor circuit for a switching element having a normally-on characteristic, or for a switching element having a normally-off characteristic in which the threshold voltage is low.
In Patent Document 1, a power supply circuit for generating a negative voltage that is to be fed to a high-side (high-voltage side) switching element, and a power supply circuit for generating a negative voltage that is to be fed to a low-side (low-voltage side) switching element are provided, wherein the high-voltage side of the high-side power supply circuit is connected to a positive terminal of the high-voltage power supply. Further, a control capacitor whose one end is connected to the low-voltage (negative voltage) side of the high-side power supply circuit is provided. The control circuit that controls on/off of the switching element is supplied with operating power supply from the control capacitor that is charged when the switching element is turned on. One example of the power supply circuit described is a negative voltage power supply formed such that electric current is flown through the capacitor via another switching element, and a zener diode is connected to the capacitor in parallel.
Patent Document 2 describes a power converter that supplies a negative voltage to a high-side normally-on switching element by using a constant voltage diode (zener diode).